docs/crd: Fix schema version check
docs/crd: Fix schema version check

The schema version check was previously broken in two ways:
* It only intended to check whether the CRD version was different from
  the most recent release, which would never be true
* Since it checked the output of [[ ! "$( COMPARISON )" ]], it was
  really just checking whether the textual output of the function was
  present rather than using the boolean value of the function.

Fix it by:
1. Checking whether the git diff from the latest tag to the target
   branch has any changes to the CRDs themselves; and
2. Fixing the comparison check to evaluate the boolean function rather
   than the output result of the function.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

michi-covalent/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,cilium/cilium